Transvenous endocardial leads may be placed inside a chamber of a patient's heart by passing the lead through a venous entry site, such as the subclavian vein or the cephalic vein, or a tributary thereof, along a venous pathway into the superior vena cava and into the right cardiac chambers. Cardiac vein leads may be advanced further, from the right atrium through the coronary sinus ostium into the coronary sinus and ultimately into one of the various cardiac veins for stimulation and/or sensing of the left heart chambers.
Cardiac lead placement is important in achieving accurate sensing of cardiac signals and proper cardiac stimulation pulse delivery for providing optimal therapeutic benefit from cardiac stimulation therapies such as cardiac resynchronization therapy (CRT). Cardiac vein leads generally need to be small in diameter to allow advancement through the cardiac veins and highly flexible in order to withstand flexing motion caused by the beating heart without fracturing. The small diameter and flexibility of the lead, however, makes advancement of the lead along a tortuous venous pathway challenging. Cardiac vein leads are generally implanted with the aid of a relatively stiff guide catheter and/or guidewire or stylet. Considerable skill and time are required to achieve proper placement of a transvenous lead along a cardiac vein site.
A subselection catheter is a catheter that is relatively smaller in diameter and more flexible than the guide catheter and is used for selecting a cardiac vein branch in which the lead will ultimately be implanted. The guide catheter is typically advanced to the os of the coronary sinus. The subselection catheter is advanced through the guide catheter into the coronary sinus and further into a selected cardiac vein branch with the use of a guidewire. When the targeted implant site is reached, the subselection catheter is removed, and the cardiac vein lead is advanced over the guidewire to the targeted implant site. The guidewire, being very flexible and having a small diameter, sometimes prolapses out of the selected vein branch, back into a larger vessel before the lead is successfully positioned at the targeted implant site. The guidewire then needs to be repositioned, with the use of the subselection catheter. Such occurrences increase the time and difficulty of the implant procedure. Improved transvenous lead delivery systems are needed for facilitating implantation of cardiac leads, particularly for implantation in cardiac vein locations.